The present invention relates to a capacitor for a magnetron of a microwave oven, and more particularly to a capacitor for a magnetron of a microwave oven capable of effectively shielding noise generated from the magnetron of the microwave oven.
Generally, various apparatuses such as home microwave oven, commercial thawing machine, industrial dryer and the like using microwave include a magnetron for generating the microwave and a capacitor for shielding noises.
The magnetron for generating the microwave is provided in an electric field space of the microwave oven. Such microwave is generated when a high voltage conducted by first and second conductive coils of a high voltage transformer attached on a substrate in the electromagnetic field space is stably supplied to the magnetron. The high voltage is generated by a conducting action of the conduction coils. Such microwave is emitted through an irradiating tube in a cooking chamber.
After passing through the irradiating tube, the microwave is emitted in the cooking chamber to heat and to cook foods placed in the cooking chamber.
The electric power line of the magnetron is mainly comprised of filament, cathode and anode. When the high voltage is applied to the magnetron to generate the microwave, the microwave having a basic frequency suitable for heating the foods as well as an unnecessarily emitted microwave, i.e. noise are generated. Then, the noise flows backward through the filament and the cathode to conduct the wave interruption to adjacent appliances.
Especially, as a television broadcasting using a satellite is widely used, the unnecessary microwave of the magnetron interacts with the broadcasting frequency so as to make an obstruction to the television receiver.
A chock coil and a capacitor connected thereto are provided to the cathode in order to reduce the reverse effect on the adjacent appliance by the noises of the magnetron. The cathode supplies electricity to the filament. The choke coil having a conductive resistance and the capacitor connected thereto absorb the unnecessary microwave, thereby preventing a leakage of the unnecessary microwave.
The choke coil is enclosed within the insulation case which is provided under the magnetron, while the capacitor is mounted outside of the insulation case. One end of the choke coil is connected to the power supply line of the filament, of which the other end is connected to a lead line of the capacitor.
A through type capacitor is widely used, which is disclosed in U.S. Pat. No. 4,811,161 (issued to Sasaki, et al on Mar. 7, 1989). In a magnetron using the through type capacitor, the choke coil is in series connected between the cathode of the magnetron and a through conduction of the through type capacitor, and the through type capacitor is inserted in a sidewall of an insulating case.
FIG. 1 is an exploded perspective view of a noise insulation apparatus including a through type capacitor according to the conventional art, and FIG. 2 is a sectional view of the through type capacitor shown in FIG. 1.
As shown in FIGS. 1 and 2, the conventional through type capacitor 10 includes an ellipse ceramic dielectric 20. The ceramic dielectric 20 has a pair of parallel thru-holes 22a and 22b. A spaced pair of electrodes 24a and 24b is provided on an upper surface of the ceramic dielectric 20 while a common electrode 26 is provided on a lower surface of the dielectric 20. The spaced electrodes 24a and 24b, and the common electrodes 26 respectively comprise thru-hole corresponding to the thru-holes 22a and 22b of the ceramic dielectric 20. The capacitor 10 further includes a grounding fitment 30 of metal material of which an ellipse opening 32 is formed at the center portion. An upstanding is formed at a desired height along a periphery of the opening on the grounding figment 30. The ceramic dielectric 30 is fixed via the common electrode 26 on the upstanding of the grounding fitment 30 in a suitable manner of soldering and the like.
Furthermore, the capacitor 10 includes a pair of conductor coated with insulation tubes 36a and 36b. The insulation tubes 36a and 36b are made of a proper material such as silicon and the like. The insulation tubes 36a and 36b are respectively inserted into the respective thru-holes 22a and 22b. The opening 32 and the through conductor 38a and 38b are respectively fitted to the respective electrode connectors 40a and 40b by press. The respective electrode connector 40a and 40b are fixed to the spaced electrodes 24a and 24b in a proper manner of soldering and the like. The through conductors 38a and 38b may be fixed to the electrode connectors 40a and 40b by the soldering and the like.
The grounding fitment 30 is formed by pressing a metal plate so that the upstanding 34 is projected to enclose the opening 32 and so that a surface of the grounding fitment 30 has a recess 42 to form an inner surface of the upstanding 34. Four thru-holes 31 are formed at four corners of the grounding fitment 30, through which the grounding fitment 30 can be attached to the shielding case 50.
The capacitor 10 further includes an insulation case 52 enclosing the ceramic dielectric 20 and an insulation cylinder 54 enclosing the thru-conductor 38a and 38b. A lower portion of the insulation case 52 is fixed to the upstanding 34 of the grounding fitment 30 while an upper portion of the insulation cylinder 54 is fixed into the recess 42 of the grounding fitment 30. The insulation case 52 and the insulation cylinder 54 are filled with insulation materials 60 and 62 such as epoxy resin and the like so that the ceramic dielectric 20 is covered with the resin or in which the resin is filled in order to be waterproof and to secure insulation property of the ceramic dielectric 20. The reference numeral 64 denotes a surface of the insulation resin in FIG. 2. The insulation case 52 and the insulation cylinder 54 are made of thermoplastic resin such as polybutylene terepthalate (PBT).
The respective through conductors 38a and 38b have respective fixing tabs 39a and 39b integrally formed at an end thereof, which are received in the insulation case 52 to apply high voltage. Since one end of the fixing tabs 39a and 39b is projected through one end of the insulation case 52, the fixing tabs 39a and 39b are easily connected to an outer terminal.
When the grounding fitment 30 is fixedly pressed to the shielding case 50, a large opening 56 corresponding to the capacitor 10 and four bearing holes 58 corresponding to four thru-holes 31 of the grounding fitment 30 are formed in the shielding case 50. Then, the bearing holes 58 face the thru-holes 31 so that the grounding fitment 30 is assembled by means of bolts with the shielding case 50.
The thru type capacitor 10 connecting the choke coil of the shielding case 50 to the outer terminal prevents the noises from being conducted through the lead line, which shields the radiated noises.
As described above, however, since the apparatus for shielding the noises from the magnetron according to the conventional art includes a plurality of assembling parts, the structure of the apparatus is complicated so that the cost of material increases as well as the assembling process becomes very difficult to reduce productivity. Furthermore, after assembling, some microwaves leak through the inserting hole of the shielding case, the thru-holes of the grounding fitment and the bearing holes of the shielding case, failing to prevent the noises to the utmost.
Therefore, the present invention has been developed to solve the above-mentioned problems.
It is an object of the present invention to provide a capacitor of a magnetron for a microwave oven capable of shielding noise such as unnecessary microwave generated from the magnetron, which has a simple structure to reduce manufacturing costs, resulting in improving productivity.
In order to accomplish the objects of the present invention, there is provided a capacitor of a magnetron for a microwave oven according to the present invention, which comprises: an insulation case; a ground plate which is combined with the insulation case, for absorbing and shielding noises such as unnecessary microwaves generated from the magnetron; and a pair of electrodes which has a fixing tap and which extends through the insulation case and the ground plate, for supplying electric current to the magnetron.
According to the first embodiment of the present invention, the insulation case is integrally formed with a pair of electrode insulating pipes. An upright portion is formed on a surface of the ground plate, in which through-holes are formed in order that the electrode insulating pipes respectively extend through the through-holes. Flanges are respectively formed around the through-holes of the ground plate.
According to the second embodiment of the present invention, the insulation case includes an upper insulation case and a lower insulation case. The upper insulation case is inserted on the upright portion of the ground plate at an upper surface of the ground plate, and the lower insulation case is inserted in a groove defined by the upright portion at a lower surface of the ground plate.
A pair of electrode insulating pipes respectively extends through the pair of extension pipes, the upper insulation case and the lower insulation case, through which the pair of electrodes respectively extends.
A space defined by the upper insulation case and the ground plate and a space defined by the lower insulation case and the ground plate are filled with insulation resin.
According to the third embodiment of the present invention, the insulation case is integrally formed with a pair of electrode insulating pipes. An upright portion is formed on a surface of the ground plate, in which a pair of through-holes is formed.
Extension pipes having a desired length are respectively mounted in the through-holes of the ground plate to extend into the insulation case, through which the electrode insulating pipes respectively extend.
According to the fourth embodiment of the present invention, the insulation case is integrally formed with a pair of electrode insulating pipes. A pair of through-holes is formed in the ground plate, in which extension pipes are respectively mounted to extend downwardly. The electrode insulating pipes respectively extend through the extension pipes.
In the second, third and fourth embodiments of the present invention, the extension pipes mounted in the ground plate are made such that a length thereof is in a range of 5 to 15 mm, and a sum of radiuses of the electrode and the extension pipe is less than 5 mm.
Meanwhile, an insulating resin is filled, or electric wave absorbing material is disposed between the insulation case and the ground plate to shield against leakage of microwave noise.
In the capacitor according to the embodiments of the present invention constructed as described above, the ground plate formed with flanges or the ground plate combined with the extension pipes can shield the microwave noise generated from the magnetron, thereby reducing electric wave obstruction applied by the noise to home appliances near the microwave oven.
Furthermore, since a part such as a ceramic dielectric adopted to the conventional capacitor is not used in the capacitor according to the present invention, it is possible to simplify the structure of the capacitor and to reduce the cost of manufacturing the capacitor. In addition, there is an advantage in that since the structure of the capacitor is simplified, a rate of assembling the capacitor is improved to increase the productivity.